Re: icase pathspec magic support in ls-tree

[Elijah Newren <newren@gmail.com>]

On Wed, Oct 12, 2022 at 11:49 PM Tao Klerks <tao@klerks.biz> wrote:
>
[...]
> I understand that case-folding is a complex topic, and doing it
> correctly in some universal sense is undoubtedly beyond me - but "my"
> context certainly does not require a high standard of correctness:
> There's a repo shared by some 1000 engineers, 200k files, lots of
> activity, three different OSes of which two default to
> case-insensitive filesystems, and every once in a while a user on
> linux creates a case-insensitive-duplicate file with differing
> content, which causes git on case-insensitive filesystems to lose the
> plot (you end up with one file's content looking like changes to the
> other file's content - "ghost changes" that appear as soon as you
> check out, that prevent you from doing a simple "pull", and that you
> just can't reset).

I've felt that same pain.

> I don't imagine I can make a perfectly correct and universal fix to
> this, but with case-insensitive matching on ls-tree in an update hook
> I believe I could reduce the frequency of this already-infrequent
> issue by at least 1000X, which would suit my purposes just fine. In my
> case filenames are mostly ansi-based, and I don't expect we've ever
> had Turkish filenames (turkish "i" being the most famous case-folding
> gotcha I think?).

How exactly would case-insensitive matching in ls-tree help you here?
Can't you write a hook without such capability that rejects such
collisions?

> I don't see this being something I can take on in my spare time, so
> for now I suspect I'll have to do a full-tree duplicate-file-search on
> every ref update, and simply accept the 1-second update hook
> processing time/delay per pushed ref :(

I don't see why you need to do full-tree with existing options, nor
why the ls-tree option you want would somehow make it easier to avoid.
I think you can avoid the full-tree search with something like:

git diff --diff-filter=A --no-renames --name-only $OLDHASH $NEWHASH |
sed -e s%/[^/]*$%/% | uniq | xargs git ls-tree --name-only $NEWHASH |
\
   sort | uniq -i -d

The final "sort | uniq -i -d" is taken from Torsten's suggestion.

The git diff ... xargs git ls-tree section on the first line will
provide a list of all files (& subdirs) in the same directory as any
added file.  (Although, it has a blind spot for paths in the toplevel
directory.)